Novel volumetric capnography indices measure ventilation inhomogeneity in cystic fibrosis

BackgroundVolumetric capnography (VCap) is a simpler alternative of multiple-breath washout (MBW) to detect ventilation inhomogeneity (VI) in patients with cystic fibrosis (CF). However, its diagnostic performance is influenced by breathing dynamics. We introduce two novel VCap indices, the Capnographic Inhomogeneity Indices (CIIs) that may overcome this limitation and explore their diagnostic characteristics in a cohort of CF patients.MethodsWe analysed 320 N2-MBW trials from 50 CF patients and 65 controls (age 4-18 years) and calculated classical VCap indices, such as slope III (SIII) and the capnographic index (KPIv). We introduced novel CIIs based on a theoretical lung model, and assessed their diagnostic performance compared to classical VCap indices and the lung clearance index (LCI).ResultsBoth CIIs were significantly higher in CF patients compared with controls (mean±SD CII1 5.9±1.4% versus 5.1±1.0%, p=0.002; CII2 7.7±1.8% versus 6.8±1.4%, p=0.002) and presented strong correlation with LCI (CII1 R2=0.47 and CII2 R2=0.44 in CF patients). Classical VCap indices showed inferior discriminative ability (SIII 2.3±1.0%/L versus 1.9±0.7%/L, P=0.013; KPIv 3.9±1.3% versus 3.5±1.2%, P=0.071), while the correlation with LCI was weak (SIII R2=0.03; KPIv R2=0.08 in CF patients). CIIs showed lower intra-subject inter-trial variability, calculated as coefficient of variation for three and relative difference for two trials, than classical VCap indices, but higher than LCI (CII1 11.1±8.2% and CII2 11.0±8.0% versus SIII 16.3±13.5%; KPIv 15.9±12.8%; LCI 5.9%±4.2%).ConclusionCIIs detect VI better than classical VCap indices and correlate well with LCI. However, further studies on their diagnostic performance and clinical utility are required.

Effect of positive end-expiratory pressure on additional passive ventilation generated by CPR compressions in a porcine model

Background Compressions given during cardiopulmonary resuscitation generate small, ineffective passive ventilations through oscillating waves. Positive end-expiratory pressure increases the volume of these passive ventilations; however, its effect on passive ventilation is unknown. Our objective was to determine if increasing positive end-expiratory pressure during cardiopulmonary resuscitation increases passive ventilation generated by compressions to a clinically significant point. This study was conducted on 13 Landrace-Yorkshire pigs. After inducing cardiac arrest with bupivacaine, cardiopulmonary resuscitation was performed with a LUCAS 3.1. During cardiopulmonary resuscitation, pigs were ventilated at a positive end-expiratory pressure of 0, 5, 10, 15, 20 cmH2O (randomly determined) for 9 min. Using the NM3 respiratory monitoring device, expired minute ventilation and volumetric capnography were measured. Arterial blood gas was obtained for each positive end-expiratory pressure level to compare the effects of positive end-expiratory pressure on carbon dioxide. Results Increasing positive end-expiratory pressure from 0 to 20 cmH2O increased the mean (SEM) expired minute ventilation from 6.33 (0.04) to 7.33 (0.04) mL/min. With the 5-cmH2O incremental increases in positive end-expiratory pressure from 0 to 20 cmH2O, volumetric capnography increased from a mean (SEM) of 94.19 (0.78) to 115.18 (0.8) mL/min, except for 15 cmH2O, which showed greater carbon dioxide exhalation with volumetric capnography compared with 20 cmH2O. PCO2 declined significantly as positive end-expiratory pressure was increased from 0 to 20 cmH2O. Conclusions When increasing positive end-expiratory pressure from 0 to 20, the contribution to overall ventilation from gas oscillations generated by the compressions became more significant, and may even lead to hypocapnia, especially when using positive end-expiratory pressures between 15 and 20.

Volumetric capnography pre- and post-surfactant during initial resuscitation of premature infants

Background Volumetric capnography allows for continuous monitoring of expired tidal volume and carbon dioxide. The slope of the alveolar plateau of the capnogram (SIII) could provide information regarding ventilation homogeneity. We aimed to assess the feasibility of measuring SIII during newborn resuscitation and determine if SIII decreased after surfactant indicating ventilation inhomogeneity improvement. Methods Respiratory function traces of preterm infants resuscitated at birth were analysed. Ten capnograms were constructed for each infant: five pre- and post-surfactant. If a plateau was present SIII was calculated by regression analysis. Results Thirty-six infants were included, median gestational age of 28.7 weeks and birth weight of 1055 g. Average time between pre- and post-surfactant was 3.2 min. Three hundred and sixty capnograms (180 pre and post) were evaluated. There was adequate slope in 134 (74.4%) capnograms pre and in 100 (55.6%) capnograms post-surfactant (p = 0.004). Normalised for tidal volume SIII pre-surfactant was 18.89 mmHg and post-surfactant was 24.86 mmHg (p = 0.006). An increase in SIII produced an up-slanting appearance to the plateau indicating regional obstruction. Conclusion It was feasible to evaluate the alveolar plateau pre-surfactant in preterm infants. Ventilation inhomogeneity increased post-surfactant likely due to airway obstruction caused by liquid surfactant present in the airways. Impact Volumetric capnography can be used to assess homogeneity of ventilation by SIII analysis. Ventilation inhomogeneity increased immediately post-surfactant administration during the resuscitation of preterm infants, producing a characteristic up-slanting appearance to the alveolar plateau. The best determinant of alveolar plateau presence in preterm infants was the expired tidal volume.

EVALUATION OF VENTILATION-PERFUSION RATIO IN CHRONIC OBSTRUCTIVE PULMONARY DISEASE

To study ventilation-perfusion ratio (VPR) in patients with chronic obstructive pulmonary disease (COPD) using method of volumetric capnography.